The objective of this proposal is to explore why phonological category processing is impaired in children with SLI by examining the role of category formation as a contributor and to test talker familiarization as a method of making phonological categories more robust. The first aim is to determine whether children with SLI can create novel talker categories (i.e., who said that utterance) as a way to explore category formation more generally. The working hypothesis is that children with SLI have difficulty creating novel categories and generalizing across diverse inputs and that this difficulty is one source of the poor phonological processing exhibited in SLI. To test this hypothesis, both children with SLI and children with typical language development (TLD) aged 9-10 will be trained to learn novel talker categories by listening to the speech of three different talkers. The second aim is to determine whether the phonological categories of children with SLI can be made more robust through familiarity with a set of talkers. The working hypothesis is that despite having formed talker categories less well than TLD children (Aim 1), children with SLI will show improved phonological processing for talkers with whom they are familiar. To test this hypothesis, both SLI and TLD children will complete a word recognition task both pre- and post-talker training (Aim 1) for both familiar and unfamiliar talkers to assess whether they show enhanced processing for familiar talkers (familiar talker advantage). At the conclusion of this project, we expect to demonstrate that phonological category representations are weak in children with SLI in part due to an inability to form robust categories that can be generalized to novel stimuli. We also expect to demonstrate that familiarity with a talker improves phonological processing, as has been shown empirically in adult populations. This research is both clinically and theoretically significant because it will provide an explanation for weak phonological categories in children with SLI and also provide evidence that these categories can be made more robust and that phonological processing can be improved through talker familiarization. These findings will have broader implications for language processing in SLI;facilitating and automating speech perception frees up cognitive resources that can be used for language comprehension. PUBLIC HEALTH RELEVANCE: We expect the findings from this research project to demonstrate the significance of the talker dimension for phonological category processing in children with SLI and to demonstrate that phonological processing can be improved for talkers who are more familiar. The proposed research has relevance to public health because understanding the reason for poor phonological category processing in children with SLI has broader implications for language processing, which relies on the ability to map acoustic signals onto linguistic messages.